For now, until the issue is fixed, the October 2018 Update has been pulled. It is no longer available for download officially, and there is no word on when it will be made available again. This is the second time Microsoft has had a major issue with a new feature update for Windows 10, the first of which happened earlier this year with the April 2018 Update, which resulted in a three week delay.

We have paused the rollout of the Windows 10 October 2018 Update (version 1809) for all users as we investigate isolated reports of users missing some files after updating.

Microsoft also advises not clean installing the new update either. It's possible that this issue will be fixed in a cumulative update, or it may be a big enough problem that requires Microsoft to compile another RTM build, just as it did with the April 2018 Update. Microsoft has been struggling to assure quality with its last few feature update releases at launch, which does not paint a positive picture for customers.

If you have already upgraded to the October 2018 Update and are experiencing issues, you should be able to recover back to the previous update by heading into Settings > Update & Security > Recovery > Go back to the previous version of Windows 10. This will restore your OS to the previous feature update that was running, likely the April 2018 Update. If you have already upgraded and found that your files are missing, Microsoft recommends you contact their support hotline at 1-800-MICROSOFT.